The present invention relates to a method for eliminating ringing of the microactuator during voice coil motor (VCM) actuator seeking in a dual-stage actuation system for a disc drive.
The density of concentric data tracks on magnetic discs continues to increase (that is, the width of data tracks and radial spacing between data tracks are decreasing), requiring more precise radial positioning of the head. Conventionally, head positioning is accomplished by operating an actuator arm with a large-scale actuation motor, such as a voice coil motor (VCM), to radially position a slider (which carries the head) on a flexure at the end of the actuator arm. The large-scale motor lacks sufficient resolution to effectively accommodate high track-density discs. Thus, a high resolution head positioning mechanism, or microactuator is necessary to accommodate the more densely spaced tracks.
One particular design for high resolution head positioning involves employing a high resolution microactuator in addition to the conventional lower resolution actuator motor, thereby affecting head positioning through dual-stage actuation. Various microactuator designs have been considered to accomplish high resolution head positioning. Microactuators typically include a stator portion and a rotor portion, the stator being attached to the flexure and the rotor supporting the slider. The rotor is movable with respect to the stator such that the slider can be positioned more precisely over a track of a disc.
The microactuator has suspension springs which can be arranged to provide linear motion of the slider by the microactuator. Linear microactuators are preferred to rotary microactuators because of their ability to use passive mechanical filtering to reject significant disturbances caused by windage excitations of the suspension load beam. However, a disadvantage of linear microactuators is the inability to control large amplitude ringing caused by the VCM actuator seeking. During seek acceleration of the VCM to coarsely position the actuator arm, the entire microactuator is in linear motion and large amplitude ringing occurs. The acceleration force of the VCM causes the suspension springs in the microactuator to oscillate the rotor carrying the slider within the stator at a resonant frequency causing the large amplitude ringing. The ringing requires some means of control to avoid excessive settling time for damping the oscillation. There exists a need in the art for the linear microactuator to balance the VCM seek acceleration and thereby eliminate the ringing without increasing the seek time for the VCM.
The present invention is a method for moving a transducing head between tracks of a disc in a dual-actuation assembly. The dual-actuation assembly has a main actuator for coarse positioning of the transducing head and a microactuator for fine positioning of the transducing head. The method comprises accelerating the main actuator during coarse positioning of the transducing head and applying control pulses to the microactuator during coarse positioning by the main actuator.
In one preferred embodiment of the present invention four control pulses are applied to the microactuator during coarse positioning by the main actuator. The application of control pulses to the microactuator eliminates ringing by the microactuator during and after coarse positioning of the transducing head.